Dodging the infinity hump

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patta
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Re: Dodging the infinity hump

Post by patta »

About darkfield at high NA
pau wrote:
Sat Dec 17, 2022 7:04 am
Likely you can have another source
No other sources, that's just me, made about 5 of those condensers last winter; confirm the weird NA 1.4, more or less measured and tested; but in that case the specimen is better to be mounted between two coverslips, that is a discrete hassle; for me was ok since I had to make two-coverslip mounts for a previous project. So the design published has lower NA but can work with a normal slide. There were some extreme condensers in the past, like "Nelson-Cassegrain" that could be used with NA 1.3 objective, but I haven't seen one for real.
Test of one model: https://www.microbehunter.com/microscop ... 28&t=14923 the apertometer says max NA~1,38 but an objective Zeiss 60x 1.40 gives darkfield (maybe they were cheating too about NA? Or the apertometer scale is a bit off).
Anyway I couldn't see astonishing improvements in resolution. Maybe with "all ducks in a row" and less vintage optics.
If somebody wants to try, I can send one or make some new to fit the condenser mount.
Pau wrote:
Sat Dec 17, 2022 9:39 am
Another approach is without condenser, profiting the total internal reflection of the light inside the glass slide laterally illuminated
That may work with the specimen in water? I tried briefly with no success. Or if we get a slide made high refractive index glass...
Last edited by patta on Sun Dec 18, 2022 7:19 am, edited 3 times in total.

patta
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Re: Dodging the infinity hump

Post by patta »

Sorry, just realized how much my previous posts were off-topic to the thread....
Anyway, my approach to the "infinity hump", (to make use of the NikonPA 20x 0.75) has been to use a standard finite microscope and mount the camera with a telephoto as tube lens, see for example link at previous post, as many others have done. No UV for now; the half-ball of the bragged condenser could be made of silica or sapphire.

Macro_Cosmos
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Re: Dodging the infinity hump

Post by Macro_Cosmos »

Pau wrote:
Sat Dec 17, 2022 9:39 am
Likely you can have another source but what I can read is:
The print in the photos works at 1.35-1.45, so it gives nice DF with a 100x 1.25
The principle stating that the inner angle of the light hollow cone must be wider that the entrance cone of the objective remains. Even here I would like to see scientific papers and also other people experiences with it, I'm pretty skeptic.

Another approach is without condenser, profiting the total internal reflection of the light inside the glass slide laterally illuminated, although it also has NA limitation, see https://www.ncbi.nlm.nih.gov/pmc/articl ... 058344.pdf I think that this can't work with oil immersion objectives although in the linked paper it's unclear
I think he is stating that in order to get darkfield with a high NA objective, a "slide" which is made from two coverslips must be used. The 1mm slide is inadequate for high NA darkfield.
This is a very interesting approach and I can totally see it to be the case, but there are severe practical limitations. How would the slide be moved, and it is unbelievably fragile? The coverslip can be sandwiched between the condenser and the objective, but moving it would surely cause frustration.

patta
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Re: Dodging the infinity hump

Post by patta »

Yes two-coverslip mounts do break easily; but they can be held by a "dummy slide".

Even more relevant to the line of the thread, just got the Winter 2022 "Quekett journal":
There is a whole article about "UV imaging of Diatoms" by a certain Jonathan M. Crowther, who modified an Olympus BHB.
Heused 365 and 313 nm; quartz slides and coverslips.
He mentions that there is no high NA darkfield condenser for UV...

Scarodactyl
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Re: Dodging the infinity hump

Post by Scarodactyl »

Huh. I would have thought the old mirror ones for darkfield fluorescence would have provided some options. Guess they aren't high NA?

patta
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Re: Dodging the infinity hump

Post by patta »

In the Quekett article he uses an old Zeiss quartz condenser with NA 0.85, likely Abbe type.
There are a lot of lenses made of fused silica / quartz in the market today, like for laser cutters, so it may be possible to put together a crude condenser similar to the Zeiss with stock components for ~100$.
I can't think of any hard obstacle in making a "cardioid" darkfield condenser for UV, just swap the glass for quartz?

Pure mirror (no glass) condensers, I've never seen one; the reflective objectives from Edmund Optics reach max NA 0,33, while Beck makes up to 0,65.

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